A new offensive is under way in the separatist region of Donetsk. The MH17 crash scene, meanwhile, has become chaotic, with international investigators finding access limited or blocked outright by rebels.

The first major fighting in Ukraine since the downing of Malaysia Airlines Flight MH17 is under way in the separatist stronghold of Donetsk, some 40 miles west of the crash site.

Various media report that artillery fire could be heard in the city near the city's railroad station. Rebel fighters gathering in the city center told Reuters that the firing was part of a new Ukrainian military offensive to root the separatists out of the city. One rebel told Agence France-Presse that the attack started at 10 a.m. local time. AFP adds that locals fled the city in cars and on foot to avoid the fighting.

The Guardian reports that Sergei Kavtaradze, of the rebels' self-proclaimed People's Republic of Donetsk, said at least four government tanks and armored vehicles had been seen in the offensive. The Ukrainian government, through a spokesman, said that "The active phase of the anti-terrorist operation is continuing." But he declined to comment on Donetsk specifically, adds the Guardian. "We are not about to announce any troop movements," he said.

The offensive comes amid international acrimony over the MH17 crash. Western leaders, including Ukraine, widely believe that the rebels, with Russian support, were responsible for shooting down the Malaysian Airlines flight on Thursday, killing all 298 people aboard.

CNN reports that both US Secretary of State John Kerry and British Prime Minister David Cameronlashed out at Moscow for Russia's alleged backing of the separatists, though they stopped just short of accusing Russia of direct responsibility for the flight downing. "This is the moment of truth for Russia. Russia is supporting these separatists. Russia is arming these separatists. Russia is training these separatists. And Russia has not yet done the things necessary in order to try to bring them under control," Mr. Kerry said.

Mr. Cameron, in an op-ed for The Times of London, wrote that the tragedy was "an outrage made in Moscow."

The rebels and Russian President Vladimir Putin deny being involved in the flight's destruction. The rebels continue to claim they lack the weaponry to bring down a jet flying at 33,000 feet, as MH17 was, despite their own earlier claims to have seized such equipment. And Mr. Putin continued to accuse Ukraine of tacit responsibility for MH17, while stressing that the investigation was of the most immediate importance, CNN writes. "We must do everything to ensure their work has full and absolute security (and) ensure necessary humanitarian corridors are provided," Putin said.

But the investigation itself is floundering. International investigators from Europe have begun to arrive on the scene, The New York Times reports, but have found their access limited, if not blocked outright, by local rebels. And with the region lacking any sort of organized bureaucracy or government organs beyond the militias, the scene has descended into chaos.

Instead of a crime scene marked with police tape, helicopters scouring its 13 square miles and specialists poring over every detail, the area was a post-Soviet free-for-all playing out in a war zone, where most of the trappings of a modern state have fallen away. With the police mostly gone, for example, militiamen now respond to traffic accidents.

“This is a disaster like no other,” said Michael Bociurkiw, the spokesman for the European security agency mission. The standard response, he said, is, “You secure the area, and then you go about the established business.”

He added: “That hasn’t happened here. And whether they even have the ability for that to happen is unclear.” ...

American intelligence officials have said a proper investigation could answer crucial questions about who is responsible for shooting down the plane, but the hopes for retrieving anything useful from the site are dwindling with each passing day.

The Wall Street Journal writes that the inability of the rebels to deal with the crash site is a byproduct of their own disorganized, fractured status. Though united by their loathing of Kiev, the rebels have little in the way of organizational structure, and even less in the way of governmental expertise.

The problem is the militants thought they would simply take over the Donetsk and Luhansk regions and then become part of Russia, said Alexander Dugin, an anti-Western, Russian imperialist political philosopher allied with the rebels, in an interview before the crash. They never expected actually to have to run the regions themselves, he said. ...

Although the militants' nominal commander is [Russian citizen Igor Girkin, who goes by the nom de guerre] Strelkov, there are a number of groups competing for influence, even in the area around the crash site. The area where the plane fell is largely controlled by Cossacks under Nikolai Kozitsyn, according to separatists and a senior Ukrainian security official in Kiev. But units from rebels loyal to Mr. Strelkov, and another rebel commander, Alexander Khodakovsky, were also on the site searching for the black boxes on Friday, according to a telephone intercept released by Ukraine's security service. The tape couldn't be independently verified.

With battles raging against Ukrainian troops, it is unlikely any of those chiefs would be willing to divert significant manpower to secure the crash site.

And, the Journal adds, local leaders and functionaries have fled amid the violence in the region, "leaving the already poorly funded police forces, sanitation crews and emergency services necessary to clean up a complex, 14-square-mile [35 square kilometer] crash site in a state of complete disarray."